This invention relates to optical logic and more particularly, to optical computing using N wavelengths to represent N values.
The development of the electronic computer was simplified tremendously by the standardization of the parts used to build it. As those parts became smaller they could be packaged together producing even smaller devices with increased functionality operating faster than their predecessors. Boolean logic gates form the basic building blocks of the electronic digital computer. The use of Boolean logic is appropriate in this application because it is difficult to move complicated data on a signal voltage line. The analog electric computer, which held data as analog voltage signals, was not successful because noise in the voltage signals corrupts the data. In the analog computer""s favor is the amount of information that is transmitted on one signal. An analog computer would have been very fast compared to the binary computer at that time.
Fiber optic cable is now the standard means of transmitting information over long distances mainly because it does not suffer from crosstalk, dispersion can be compensated for and information being moved optically can be multiplexed in the wavelength domain. Wavelength division multiplexing (WDM) allows signals transmitted at different wavelengths (or colors) to be transmitted simultaneously down one optical fiber and operated on independently. Consequently, one optical fiber can carry significantly more information than a metal wire based on today""s technology.
This advantage has been exploited by long distance bandwidth providers but it has not gained acceptance for optical computing applications. The concept of optical logic gates has been presented in U.S. Pat. No. 5,999,283. The patent describes a method of producing optical logic gates. The gates presented combine semiconductor optical amplifiers (SOA) and Mach Zehnder interferometers (MZI). The components it presents are based on Boolean logic which does not take advantage of wavelength division multiplexing.
In U.S. Pat. No. 4,262,992 a general design is presented that allows many different optical logic gates to share their footprint on the same substrate. This device also uses an interferometer producing constructive and destructive interference but in this case the interference is controlled with electrodes making it possible to reconfigure the substrate as required.
In Choo, Detofsky and Louri, Sep. 10, 1999, Applied Optics, Volume 38, Number 26, p 5594 to 5604, an optical processor is presented in which WDM and polarization effects are both used to enhance processing. This system is limited to using bulk optics, which limit the size and therefore complexity of the system. A two dimensional pixilated grid is used to polarization encode the data and wavelength is used to differentiate between different sets of data. Data is manipulated with logic gates that use polarization to attenuate the signal. This architecture cannot be used with fiber optic waveguides at this time due to the difficulty of integrating small polarization controlling components in the waveguides.
The field of optical computing is still developing and will likely see applications in smaller scale data networks. One current approach to smaller scale networks uses a configurable network architecture where destinations on the network are wavelength specific and the sources are tunable. This allows any source to selectively send information to any location in the network provided that only one source tries to send data to one receiver at one time. This network architecture is also limited in that the signals are not separated by wavelength until they reach their destination. Therefore, as the device is proposed in STARNET: A Multi-gigabit-per-second Optical LAN Utilizing a Passive WDM Star, Kazovsky, Poggiolini, Journal of Lightwave Technology, Vol. 11, No. 5/6 1993, p 1009-1027, every receiver can see all of the information. The individual receivers must be tuned to read only the information that is intended for them. Also, the signals are attenuated when they pass through the star coupler.
In order to overcome these and other limitations of the prior art, it is an object of the invention to provide an optical digital logic architecture that utilizes the wavelengths of light to perform data representation and manipulation. This architecture is referred to as the N-valued optical digital logic system. It has applications in optical data storage and optical computing.
This invention relates to optical communication, data storage, and optical computing. It describes a means of processing and encoding data in the optical domain. As an optical communications design invention it describes an architecture supporting N wavelengths of light representing digital data in an N-valued logic system comprising:
a plurality of optical components, each component having an input port and an output port and for operating on a light signal received at the input port in accordance with a transfer function from a plurality of predetermined transfer functions. The light within the signal at a predetermined wavelength of the N wavelengths corresponds to a predetermined value among the N values and wherein N is at least 2.
In the proposed N-valued optical digital logic system, these transfer functions are applied in the optical domain. Since the input signals and output signals are both optical signals, the output signal of a first gate can be used as an input signal to a second gate.
Additionally, the architecture supports two wavelengths, wherein a first wavelength corresponds to a xe2x80x9c0xe2x80x9d and a second other wavelength corresponds to a xe2x80x9c1xe2x80x9d. It then uses a binary interface to convert the N wavelength optical signal into an intensity encoded optical signal having two intensity levels representative of a 1 and a 0, respectively.
The optical logic gate transfer functions are given below. These gates can be combined to produce optical circuits. Alternatively, these gates can be used for simpler optical applications.
The invention also allows the use of multiple wavelengths to store data. That is, the data is stored in an appropriate medium in which one wavelength returns when a source hits it. Since a variety of wavelengths can be returned the presence of the one returned wavelength indicates the value of the data.
In accordance with another embodiment of the invention there is provided an optical logic system having N symbols wherein each symbol is represented by a wavelength of light comprising:
a. an optical component including:
b. a first port for receiving a first optical signal at any of the N wavelengths representative of the N symbols;
c. an output port; and
d. an optical circuit for receiving the first optical signal at any of the N wavelengths, for varying the first optical signal in accordance with a predetermined transfer function and for providing the second optical signal representative of one of the N symbols to the output port, the predetermined transfer function a same function for each of the N wavelengths.